U.S. Pat. No. 6,333,775, which is incorporated herein by reference, discloses a sealing assembly for use in an EUV lithography apparatus. The assembly is arranged for sealing a respective gap extending between an optics zone and a substrate zone, or a gap between the optics zone and a reticle zone, of the EUV lithography apparatus. The gaps are provided for maintaining different parts of the apparatus vibrationally isolated from each other, particularly to shield the projection optics from environmental vibrations. The sealing assembly serves to seal the respective gap to prevent contamination, emanating from the wafer zone or reticle zone, from transmitting via the gap into the other zones of the apparatus. The seal assemblies serve to maintain the zones at appropriate vacuum pressures.
In U.S. Pat. No. 6,333,775, three different sealing assemblies are proposed for sealing the gaps. A first sealing assembly includes a horizontal seal and a vertical seal which completely close off the gap, so that no particles will be transmitted through the slit. However, a disadvantage of this first assembly is that the two seals provide a relatively stiff connection, which leads to a poor vibration isolation.
In a second embodiment shown in U.S. Pat. No. 6,333,775, the disadvantage is partly removed by the application of a sheet of flexible polymer instead of the horizontal seal. However, such a sheet is relatively stiff in a rotational direction. Therefore, substantially no rotation isolation can be achieved.
A third seal assembly of U.S. Pat. No. 6,333,775 includes a horizontal steel plate, that extends such that the gap is narrowed to 0.008 inch. In this third embodiment, some vibrational isolation of different components of the apparatus can be achieved in all directions. However, the third embodiment can not cope with relatively large vibrations. The small gap is relatively hard to maintain during the full operational life of a industrial vacuum machine. Furthermore, a relatively large amount of particles can be transmitted via such a slit, particularly in case there is a relatively large pressure difference between the zones that are in fluid connection with the slit.